The invention relates to a photographic camera of automatic exposure control type, and more particularly, to such camera having an electrical shutter of an electromagnetic release type which is provided with a front cover movable between a first position in which it covers a taking lens and a second position in which it permits the taking lens to be exposed.
As is well recognized, a taking lens in a usual camera is coverd by a lens cap to protect it from the deposition of dusts or fingerprints thereon or its abrasion except when the camera is used to take a picture. However, a lens cap is easily lost. The present applicant has previously proposed a photographic camera of automatic exposure control type which is provided with a slidable front cover capable of covering at least the taking lens when the camera is not in use (see U.S. Ser. No. 969,776 and German patent application P2901491.3).
Before proceeding with the description of the present invention, a photographic camera of automatic exposure control type having such a front cover will be described with reference to FIGS. 1 to 3. In these Figures, there is shown camera 1 which has body 5 of a rectangular configuration having its top and bottom closed by upper and lower panels 6, 7. Body 5 includes front wall 5a, the central portion 5c of which is raised higher than the remainder and receives taking lens 2 therein. On the upper, left-hand side thereof, the front wall is formed with window 18 for passing input light onto light receiving element CdS (see FIG. 5) which is provided for purpose of photometry. Body 5 includes top wall 5b which is also centrally raised and in which finder objective lens 3 and eyepiece (not shown) are disposed.
Front cover 4 is formed of a sheet material which is folded to define front plate 4a, top plate 4b and rear plate (invisible in FIGS. 1 to 3) which extend along the front, the top and the rear surface of body 5 inclusive of front wall 5a and the central raised portion of top wall 5b. In its lower end, front plate 4a is formed with guide slot 8 which is elongate in the lengthwise direction of body 5. Guide pin 9 which is fixedly mounted on the lower end of front wall 5a is fitted into guide slot 8, thereby allowing cover 4 to be moved between a first position shown in FIG. 1 in which it covers the taking lens to disable a photographing operation and a second position shown in FIG. 2 in which it is displaced to the right to expose taking lens 2, thus enabling a photographing operation. In the example shown, cover 4 has a lateral width which prevents its projection beyond the extremity of camera 1 in its second position. Disposed in top wall 5b is stop member 17 which is adapted to move upwardly for abutment against the inner end face of cover 4 when the latter is displaced to its second position and which is engageable with a slot, not shown, formed in the inner surface of top plate 4b to prevent an unintended movement of cover 4.
Film rewind knob 10 is disposed in upper panel 6 toward its right-hand end, while shutter release button 11, sight window 13a associated with film frame counter 13 and index 14 are disposed thereon toward the left-hand end thereof. Film winding knob 12 is disposed on the rear side of body 5 toward the left-hand end thereof. In addition, synchro contact socket 15 is disposed in the left-hand portion of front wall 5a for permitting a flashlight photographing operation. The camera also includes rear lid 16 which is hinged on the left-hand sidewall of body 5 for pivotal movement.
FIG. 4 shows an electrical shutter mechanism of an electromagnetic release type which may be incorporated into the camera described above. Referring to FIG. 4, there is shown disc-shaped shutter drive member 21 which is fixedly mounted on single rotatable shaft 22. Prime mover spring 23 disposed on shaft 22 has its one end 23a anchored to drive member 21 and its other end fixedly 23b connected with charging member 29 which is driven for rotation in response to a film winding operation. In this manner, prime mover spring 23 is charged as a film is being wound, thus urging shutter drive member 21 to rotate in the counter-clockwise direction. However, before the shutter is operated, the resulting rotation of drive member 21 is prevented by the abutment of arm 21a radially extending from drive member 21 against bevelled edge 25a of member 25 which is pivotally mounted at 24 and which defines a start position for the rotation of drive member 21. Thus, drive member 21 is maintained at rest at the start position.
Bevelled edge 25a is formed on one end of member 25 while its other end 25b is held attracted to shutter release electromagnet Mg1, which comprises a release electromagnet of a known form including a permanent magnet. Member 25 is normally urged by spring 30 to rotate clockwise about pivot 24, whereby end 25b is held attracted by electromagnet Mg1 while bevelled edge 25a is engaged by arm 21a to maintain shutter drive member 21 at rest at its start position.
Located on the path of rotation of arm 21a is controller 26a which is formed by one arm of detent member 26 which is effective to determine an exposure period. Detent member 26 is pivotally mounted at 27, and is urged by spring 28 to rotate counter-clockwise about pivot pin 27. As a consequence, armature 26b formed on the other end thereof moves into abutment against shutter controlling electromagnet Mg2 and is held attracted thereto during the operation of the shutter.
Drive pin 31 is fixedly mounted on the upper end face of shutter drive member 21 adjacent to the periphery thereof, and fits in elongate slot 32b formed in horizontally extending portion 32a which is formed at the lower end of connecting rod 32. Rod 32 is pivotally mounted on pin 33, and fixedly carries shutter blade drive pin 34 on is upper end which fits in elongate slots 37a, 38a formed in one end of both shutter blades 37, 38. Both shutter blades 37, 38 have their one end pivotally mounted on pins 35, 36, and are shown in their position closing taking light path 39 in FIG. 4. Shutter blades 37, 38 constitute together a so-called vario type shutter, and operate to open or close light path 39 when shutter drive member 21 is driven by the resilience of prime mover spring 23 to rock connecting rod 32 about its pin 33 through drive pin 31.
The described shutter mechanism is automatically controlled by an electrical shutter circuit which is shown in FIG. 5. In FIG. 5, power source E has its positive terminal connected with positive bus E1 and its negative terminal connected with negative bus E2. A series circuit including release switch SW1, which is interlocked with release button 11, capacitor C1 and resistors R2, R3 is connected across the pair of buses as is another series circuit including disconnection switch SW2, which is interlocked with a film winding mechanism to disconnect the shutter circuit from the power supply when the film winding operation is completed, resistor R4, and starting transistor Tr1 of NPN type. Also connected across the pair of buses E1 and E2 are a series circuit of PNP transistor Tr3, which is effective to maintain the circuit connected with the power supply, and resistor R5, a further series circuit including resistor R6 and NPN trigger transistor Tr4, still another series circuit including resistor R9, electromagnet Mg1 and capacitor C2, and an additional series circuit including electromagnet Mg2, shunted by counter e.m.f conducting capacitor C4, and NPN switching transistor Tr7.
Resistor R1 having an increased resistance is connected between the junction between release switch SW1 and capacitor C1 and bus E2 for causing a discharge of capacitor C1. Transistor Tr1 has its base connected with the junction between resistors R2 and R3, its emitter connected with bus E2 and its collector connected with resistor R4. NPN transistor Tr2 is connected in shunt with transistor Tr1, and has its collector connected with the collector of transistor Tr1, its emitter connected with bus E2 and its base connected with the collector of transistor Tr3. The base of transistor Tr3 is connected with the junction between resistor R4 and switch SW2, and its emitter is connected with bus E1, while its collector is connected with resistor R5.
Transistor Tr4 has its base connected with the collector of transistor Tr3, its emitter connected with bus E2, and its collector connected with one end of resistor R6, which has its other end connected with bus E1. The junction between resistor R6 and the collector of transistor Tr4 is connected with another bus E3. Connected across buses E1 and E3 are a photometric control circuit and a drive circuit for electromagnet Mg1, both of which form the heart of the electrical shutter circuit. Thus, transistor Tr4 effectively operates as a power switch and a trigger switch for the photometric control circuit.
The drive circuit for electromagnet Mg1 comprises a series circuit including PNP transistor Tr5 and resistor R8 connected across buses E1 and E3, and NPN transistor Tr6 which is connected in shunt with the series combination of electromagnet Mg1 and capacitor C2. Specifically, transistor Tr5 has its base connected with bus E3 through resistor R7, its emitter connected with bus E1, and its collector connection with bus E3 through resistor R8. Transistor Tr6 has its base connected with the collector of transistor Tr5, its emitter connected with bus E2 and its collector connected with bus E1 through resistor R9. Capacitor C2 is normally charged from power supply E through resistor R9 and electromagnet Mg1, and is caused to discharge rapidly through electromagnet Mg1 and transistor Tr6 as transistor Tr4 is turned on to cause a conduction of transistors Tr5 and Tr6, thus counteracting or cancelling the force of attraction applied by a permanent magnet contained in the release electromagnet which forms the electromagnet Mg1.
The photometric control circuit comprises a series circuit of photometric, light receiving element CdS which is disposed adjacent to window 18 mentioned above, and timing capacitor C3, and another series circuit connected in shunt with element CdS and including flash photography switch SW7 and timing resistor R13 which is utilized to determine an exposure period during a flash photography. These series circuits form a time constant circuit which determines an exposure period and which is connected across buses E1, E3. In addition, the control circuit includes a voltage divider formed by a series combination of variable resistor VR1 and resistor R10, and comparator CP, all connected across the pair of buses E1 and E3.
Light receiving element CdS is adapted to receive reflective light from an object being photographed which passes through window 18, and is adapted to exhibit a resistance which varies in accordance with the brightness level of the reflective light, thus establishing the resistance of time constant circuit. The junction between element CdS and capacitor C3 is connected with one input of comparator CP. Switch SW7 is turned on as the shutter is operated when an electronic flash is connected with synchro circuit 15. When it is turned on, resistor R13 is connected in parallel with element CdS to permit the shutter to be closed at an earlier timing than that determined by the combination of element CdS and capacitor C3 alone. Usually, this earlier timing is chosen to be on the order of 1/30 to 1/60 second.
The junction between variable resistor VR1 and resistor R10 is connected with the other input of comparator CP to determine the level at which comparator CP operates to reverse its output. Comparator CP operates to supply an output voltage to the base of switching transistor Tr7 through resistor R11 whenever transistor Tr4 is turned on. Consequently, transistor Tr7 is turned on to operate the shutter. When capacitor C3 in the time constant circuit is charged to a given level, comparator CP operates to reverse its output voltage, whereby an output voltage ceases to be applied to the base of transistor Tr7, thus turning it off.
The operation of the described electrical shutter will now be described with reference to FIGS. 4 and 5. FIG. 4 shows the shutter when it is charged after a film winding operation. Since prime mover spring 23 is charged, it urges shutter drive member 21 to rotate counter-clockwise. However, member 25 which is constrained by shutter release electromagnet Mg1 has its bevelled edge 25a located in the path of rotation of arm 21a to block a movement thereof, so that shutter drive member 21 remains at rest at the start position.
To take a picture, the front cover 4 shown in FIG. 2 is moved to its open position and shutter button 11 is depressed. In response thereto, release switch SW1 is closed. Then, in the electrical circuit shown in FIG. 5, differentiated pulse is produced by capacitor C1 and is applied to the base of starting transistor Tr1, which is then turned on. This causes transistor Tr3 to be turned on also, whereby both transistors Tr2 and Tr4 are also turned on. When shutter button 11 is released subsequently to open switch SW1 to thereby turn transistor Tr1 off, transistor Tr3 maintains its conductive condition, so that transistors Tr2 and Tr4 remain on, thus maintaining the connection of the shutter circuit with the power supply.
When transistor Tr4 conducts, bus E3 is fed from power supply E, so that transistors Tr5 and Tr6 are immediately turned on. Comparator CP produces an output voltage which is applied to the base of transistor Tr7 to turn it on, whereby electromagnet Mg2 is energized. When transistor Tr6 conducts, capacitor C2 momentarily discharges through shutter release electromagnet Mg1, thus counteracting the force of attraction thereof. In response to such demagnetization, arm 25b of member 25 is freed, whereby the resilience of spring 23 which acts on arm 21a causes member 25 to rotate counter-clockwise about its pivot pin 24, thus moving bevelled edge 25a out of engagement with arm 21a to permit a counter-clockwise rotation of shutter drive member 21 under the resilience of spring 23, thus starting the shutter to run.
As shutter drive member 21 begins to rotate counter-clockwise, its integral drive pin 31 rocks connecting rod 32 clockwise, whereby shutter blades 37, 38 being to open in accordance with the displacement of connecting rod 32 until taking light path 39 is fully opened at a position where arm 21a is blocked by controller 26a on detent member 26.
The photometric control circuit begins to operate at the same time as the electromagnet Mg1 is energized by a discharge current from capacitor C2. The control circuit operates by integrating the amount of reflective light from an object being photographed by the time constant circuit comprising capacitor C3 and element CdS, with a voltage representing the integral applied to one input of comparator CP. In this manner, the time constant of this circuit, which controls the time required for capacitor C3 to be charged to a given level, determines a proper exposure period as is well recognized.
When an electronic flash is connected with the synchro socket 15, switch SW7 is turned on as the shutter is operated, so that a parallel combination of resistor R13 and element CdS is connected with capacitor C3 to provide an exposure period on the order of 1/30 to 1/60 second as mentioned previously.
As capacitor C3 is charged and reaches a voltage level which is equal to that at the junction between resistors VR1 and R10, comparator CP operates by interrupting its output voltage, whereby electromagnet Mg2 is deenergized to cause the shutter to be closed. When electromagnet Mg2 is deenergized, armature piece 26b on detent member 26 is no longer constrained, and thus the resilience of prime mover spring 23 is effective to cause arm 21a to drive controller 26a out of the path of rotation thereof, thus permitting a further counter-clockwise rotation of shutter drive member 21 until the start position shown in FIG. 4 is reached to complete one revolution. Thereupon arm 21a turns disconnection switch SW2 on, thus turning transistors Tr2 to Tr6 off. The permanent magnet contained in the electromagnet Mg1 attracts the other end 25b of member 25, whereby bevelled edge 25a is returned to its initial position, thus abutting against arm 21a to stop the rotation of drive member 21. After disengagement of arm 21a from controller 26a, shutter blades 37, 38 rotate counter-clockwise to close taking light path 39, which is completely closed at the stop position of drive member 21.
When a picture is taken by an automatic exposure process accomplished by the electrical shutter, a film winding operation takes place, which charges prime mover spring 23 in preparation to taking another picture.
The above description covers the operation of a camera having front cover 4 and an electrical shutter of electromagnet release type which has been previously proposed by the present applicant.
In a camera of automatic exposure control type and having a front cover which is capable of being opened and closed, it is desirable to prevent an unintended shutter release during the portable use thereof in order to prevent a wasteful photographing operation and power dissipation. This can be achieved by disabling a shutter release operation when the front cover is closed. It is also advantageous to prevent the rear lid from being opened inadvertently when the front cover is in its open position.
However, when the described camera is provided means which achieves such objectives, an inconvenience is caused during a film loading operation. Specifically, the rear lid must be opened to permit a film loading. This requires that the front cover be moved to its closed position, but this disables a shutter release operation. Because the shutter release operation is disabled, the shutter cannot be operated, preventing a film winding mechanism from operating. Hence a leader portion of the film cannot be wrapped around a film take-up spool.
To remove the described difficulty, an arrangement must be made to permit a shutter operation when the front cover is closed and the rear lid of the camera is opened. However, under this condition, because the front cover is closed, no light impinges upon the light receiving element, so that an exposure period of an increased length would result. Hence, there is a need to permit a shutter operation with a reduced exposure period under the condition mentioned above.